To make possible a stable beam path whose optical properties are to be largely independent of temperature changes, temperature regulation or corresponding corrections are necessary in particular when optically active components are used, for example in the case of acoustooptical tunable filters (AOTFs). AOTFs can be used for wavelength-selective coupling of light from multi-wavelength lasers into an optical assemblage, for example a confocal scanning microscope. In this context, the light is refracted at the sound waves passing through the AOTF. The drive power levels of the ultrasonic waves are approximately 1 W; the energy of the mechanical sound waves is ultimately converted into thermal energy, which results in heating of the optical component. In addition, the component is further heated by absorption of the light rays passing through the component. Usually, in the event of an interruption of the light that is to be coupled into a confocal scanning microscope, the drive energy or sound waves of the AOTF are switched off and the light that is to be coupled in is completely interrupted, for example with a shutter preceding the AOTF. If the interruption lasts a long time, the optical component has a different optical property due to the temperature change, thus disadvantageously influencing principally the efficiency with which light is coupled in.
Methods and apparatuses of the generic type are known from practical use. The reader is referred, purely by way of example, to DE 198 27 140 A1, which discloses a laser scanning microscope having an AOTF. The AOTF known from this apparatus has in its vicinity a temperature sensor and/or a heating system or cooling system. Either the AOTF is regulated to a constant temperature with the aid of the heating system or cooling system, the temperature sensor serving as a signal generator for a corresponding control loop; or alternatively, the instantaneous temperature of the AOTF is measured, and on the basis of previously stored correction curves, the AOTF frequency is adjusted and optimized in a predefined frequency window as a function of the temperature.
The approach known from the existing art requires a temperature sensor directly on the optical component or at least in its immediate vicinity, and the temperature sensor must have sufficient temperature accuracy. The use of a heating system or cooling system moreover requires additional space in terms of design, which is not always available especially in complex optical assemblages.